In, for example, integrated drive generators (IDG's) and constant speed drives (CSD's) used, for example, in aircraft constructions, generally a dual pump arrangement is provided, with the pump arrangement including, for example, a centrifugal pump means for charge oil to hydraulic logs and supply pressure for a speed control function, and a positive displacement pump means for circulating oil through, for example, an external oil cooler, circulating oil filter, etc.
In, for example, U.S. Pat. No. 3,154,921, a dual positive displacement pump arrangement for a steering system is proposed, with the pumps respectively forming a fluid source and with a control valve arrangement being provided which is adapted to ensure a substantially constant volume of fluid supply when both pumps are in operation regardless of the speed of the drive source for the pumps.
U.S. Pat. No. 4,680,920 proposes a pump arrangement for an automatic transmission wherein a bypass passage is provided which branches off an outlet passage from a torque converter of the transmission at a position upstream of an oil cooler, with a bypass valve being associated with the bypass passage and being adapted to open the bypass passage during warming up of the automatic transmission to permit at least a portion of the oil discharged from the torque converter to be returned to an oil tank without passing through an oil cooler.
While the above proposed pump arrangements are more or less effective in providing a controlling function, neither of the pump arrangements provide for a priority diversion of hydraulic fluids handled in dependence upon an operating condition of one of the pumps nor provide any approach for regulating a flow from a centrifugal pump with a sharing of a flow from a centrifugal pump and a vane pump to separate hydraulic circuits in the hydraulic system.